http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53386
Bug #: 53386
Summary: Bad assembly code produced for m68000
Classification: Unclassified
Product: gcc
Version: 4.6.4
Status: UNCONFIRMED
Severity: blocker
Priority: P3
Component: target
AssignedTo: unassig...@gcc.gnu.org
ReportedBy: lja...@gmail.com
Hi,
I'm currently using gcc 4.2.4 to build uClinux for a 68000 target (68HC000
cpu).
I've update my toolchain to newer tool versions but now gcc (4.6.4) is
producing bad assembly for this target.
I'm almost sure that it is producing only 68020 assembly code and/or ignoring
the -m68000 switch (I checked that when specifying -m68000 or -m68020 gcc is
producing the same assembly code).
Here is a simple testcase (a line from the kernel where my system was hanging):
C instruction (from 'proc_net_ns_init' function):
[...]
memcpy(netd->name, "net", 4);
[...]
4.2.4 assembly output:
[...]
60: 157c 006e 004d moveb #110,%a2@(77)
66: 157c 0065 004e moveb #101,%a2@(78)
6c: 157c 0074 004f moveb #116,%a2@(79)
72: 422a 0050 clrb %a2@(80)
[...]
4.6.4 assembly output:
[...]
42: 217c 6e65 7400 movel #1852142592,%a0@(77)
48: 004d
[...]
Since the opcode movel has an odd displacement, it is causing an address/bus
error exception, halting the cpu.
Another difference I've noticed while tracing the above issue, is the way
parameters are placed in the stack for the function call:
4.2.4 assembly:
[...]
movel absolute_address,%sp-
[...]
4.6.4 assembly:
[...]
moveaw value1,%a0
addal value2,%a0
movel %a0@,%sp-
[...]
This is not critical but at a first look, it look it has slower execution and
produces larger code (is this correct?).
Command line used in this test (from the kernel build):
m68k-uclinux-gcc -m68000 -Wp,-MD,net/sunrpc/.rpc_pipe.o.d -isystem
/usr/local/lib/gcc/m68k-uclinux/4.5.1/include
-I/root/m68k/20120401/uClinux-dist/linux-3.x/arch/m68k/include
-Iarch/m68k/include/generated -Iinclude -include
/root/m68k/20120401/uClinux-dist/linux-3.x/include/linux/kconfig.h -D__KERNEL__
-Wall -Wundef -Wstrict-prototypes -Wno-trigraphs -fno-strict-aliasing
-fno-common -Werror-implicit-function-declaration -Wno-format-security
-fno-delete-null-pointer-checks -O2 -pipe -DUTS_SYSNAME=\"uClinux\"
-D__uClinux__ -fomit-frame-pointer -Wdeclaration-after-statement
-Wno-pointer-sign -fno-strict-overflow -DCC_HAVE_ASM_GOTO
-D"KBUILD_STR(s)=#s" -D"KBUILD_BASENAME=KBUILD_STR(rpc_pipe)"
-D"KBUILD_MODNAME=KBUILD_STR(sunrpc)" -c -o fs/proc/proc_net.o
fs/proc/proc_net.c
Anyone knows what is the latest gcc version where code for 68000 is still ok?
(I didn't want to go and build version by version until I find the one that's
broken...)
Regards,
Luis Alves
